Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Exemplary embodiments provide a technique to reduce the traffic between
storage devices during data migration. In one embodiment, a system
comprises a plurality of storage systems which are operable to migrate a
set of primary and secondary volumes between the storage systems by
managing and copying, between the storage systems, a plurality of same
data and a plurality of difference data between the primary and secondary
volumes and location information of each of the plurality of difference
data, the location information identifying a location of the difference
data in the primary or secondary volume associated with the difference
data. Each secondary volume which corresponds to a primary volume, if
said each source secondary volume contains data, has a same data as the
primary volume and, if said each secondary volume is not synchronized
with the primary volume, further has a difference data with respect to
the primary volume.

Claims:

1. A system comprising: a plurality of storage systems which are operable
to migrate a set of primary and secondary volumes between the plurality
of storage systems by managing and copying, between the plurality of
storage systems, a plurality of same data and a plurality of difference
data between the primary and secondary volumes and location information
of each of the plurality of difference data, the location information
identifying a location of the difference data in the primary or secondary
volume associated with the difference data; wherein each secondary volume
which corresponds to a primary volume, if said each source secondary
volume contains data, has a same data as the primary volume and, if said
each secondary volume is not synchronized with the primary volume,
further has a difference data with respect to the primary volume.

2. The system according to claim 1, wherein the plurality of storage
systems are operable to copy each same data of the plurality of same data
from a source primary volume for said each same data to a corresponding
target primary volume and a corresponding target secondary volume.

3. The system according to claim 2, wherein the corresponding target
primary volume and the corresponding target secondary volume are disposed
in a target storage system; and wherein the plurality of storage systems
are operable to copy each difference data of the plurality of difference
data from a source secondary volume for said each difference data to a
corresponding target secondary volume, if data in the corresponding
target secondary volume has not been updated in the target storage system
since the difference data is stored in the source secondary volume.

4. The system according to claim 1, wherein the plurality of storage
systems are operable to copy each difference data of the plurality of
difference data from a source secondary volume for said each difference
data to a corresponding target secondary volume.

5. The system according to claim 1, wherein the location information of
each difference data of the plurality of difference data comprises a
delta bitmap identifying the location of said each difference data in the
primary or secondary volume associated with the difference data.

6. The system according to claim 5, wherein a source primary volume has a
plurality of corresponding source secondary volumes to establish multiple
pairs for the same source primary volume, each pair of the multiple pairs
having a delta bitmap identifying the location of any difference data for
said each pair; and wherein migrating the source primary volume and the
plurality of corresponding source secondary volumes comprises copying
same data and difference data for the source primary volume and the
plurality of corresponding source secondary volumes, to a target primary
volume and a plurality of corresponding target secondary volumes, based
on the delta bitmap of each pair of the multiple pairs.

7. The system according to claim 1, wherein for migration from a source
primary volume and a corresponding source secondary volume which
establish a pair of source volumes in a source storage system to a target
primary volume and a corresponding target secondary volume which
establish a pair of target volumes in a target storage system, the
plurality of storage systems are operable to: manage local copy
difference information between each primary volume and each corresponding
secondary volume which establish a pair; manage migration progress
between each source volume and each corresponding target volume using a
migration progress management table which shows, for an address of one or
both of the volumes of each pair, a migration progress delta which is
initially set to YES and is changed to NO when a copy for migration from
source to target is finished on the address; if the migration progress
delta for the source primary volume is YES, copy data from the source
primary volume to the target primary volume and change the migration
progress delta of the address of the target primary volume to NO, and, if
the local copy difference information indicates there is no difference
data between the target primary volume and the target secondary volume,
copy the data from the source primary volume to the target secondary
volume and change the migration progress delta of the address of the
target secondary volume to NO; and if the migration progress delta for
the source secondary volume is YES, copy data from the source secondary
volume to the target secondary volume and change the migration progress
delta of the address of the target secondary volume to NO.

8. The system according to claim 1, wherein each storage system includes
a pool for storing the difference data for the volumes in said each
storage system; and wherein the location information for each difference
data identifies the location of said each difference data in the pool.

9. The system according to claim 8, wherein the location information for
each difference data is associated with a secondary volume which has said
each difference data with respect to a corresponding primary volume; and
wherein the plurality of storage systems are configured, for migration
from a source primary volume and a corresponding source secondary volume
which establish a pair of source volumes in a source storage system to a
target primary volume and a corresponding target secondary volume which
establish a pair of target volumes in a target storage system, to: manage
local copy difference information between each primary volume and each
corresponding secondary volume which establish a pair; and if the local
copy difference information indicates there is difference data between
the pair of source volumes, copy the difference data for the pair of
source volumes from a pool in the source storage system to a pool in the
target storage system using the location information associated with the
source secondary volume of the pair of source volumes.

10. The system according to claim 9, wherein a source primary volume has
a plurality of corresponding source secondary volumes to establish
multiple pairs for the same source primary volume, each corresponding
source secondary volume being associated with the location information
for any difference data with respect to the source primary volume; and
wherein the plurality of storage systems are configured, after the
difference data is copied from the pool in the source storage system to
the pool in the target storage system, to associate the location
information for the difference data in the pool in the target storage
system with each corresponding target secondary volume in the target
storage system.

11. A first storage system in a system of a plurality of storage systems,
the first storage system comprising a processor; a memory; and a
migration control module, the migration control module being configured
to: migrate a set of source primary and secondary volumes from the first
storage system to one or more target storage systems by managing and
copying, between the first storage system and the one or more target
storage systems, a plurality of same data and a plurality of difference
data between the source primary and secondary volumes and location
information of each of the plurality of difference data, the location
information identifying a location of the difference data in the source
primary or secondary volume associated with the difference data; wherein
each source secondary volume which corresponds to a source primary
volume, if said each source secondary volume contains data, has a same
data as the source primary volume and, if said each source secondary
volume is not synchronized with the source primary volume, further has a
difference data with respect to the source primary volume.

12. The first storage system according to claim 11, wherein the migration
control module is configured to copy each same data of the plurality of
same data from a source primary volume for said each same data to a
corresponding target primary volume and a corresponding target secondary
volume in a target storage system; and wherein the migration control
module is configured to copy each difference data of the plurality of
difference data from a source secondary volume for said difference data
to a corresponding target secondary volume in a target storage system.

13. The first storage system according to claim 11, wherein the location
information of each difference data of the plurality of difference data
comprises a delta bitmap identifying the location of said each difference
data in the source primary or secondary volume associated with the
difference data; wherein one source primary volume has a plurality of
corresponding source secondary volumes to establish multiple pairs for
the same source primary volume, each pair of the multiple pairs having a
delta bitmap identifying the location of any difference data for said
each pair; and wherein migrating the source primary volume and the
plurality of corresponding source secondary volumes comprises copying
same data and difference data, for the source primary volume and the
plurality of corresponding source secondary volumes, to a target primary
volume and a plurality of corresponding target secondary volumes in a
target storage subsystem, based on the delta bitmap of each pair of the
multiple pairs.

14. The first storage system according to claim 11, wherein for migration
from a source primary volume and a corresponding source secondary volume
which establish a pair of source volumes in the first storage system to a
target primary volume and a corresponding target secondary volume which
establish a pair of target volumes in a target storage system, the first
storage system further comprises a local copy control module configured
to manage local copy difference information between each source primary
volume and each corresponding source secondary volume which establish a
pair; and wherein the migration control module is configured to: manage
migration progress between each source volume and each corresponding
target volume using a migration progress management table which shows,
for an address of one or both of the source volumes of each pair, a
migration progress delta which is initially set to YES and is changed to
NO when a copy for migration from source to target is finished on the
address; if the migration progress delta for the source primary volume is
YES, copy data from the source primary volume to the target primary
volume and change the migration progress delta of the address of the
target primary volume to NO, and obtain from the target storage system
local copy difference information between the target primary volume and
the target secondary volume, and, if the obtained local copy difference
information indicates there is no difference data between the target
primary volume and the target secondary volume, copy the data from the
source primary volume to the target secondary volume and change the
migration progress delta of the address of the target secondary volume to
NO; and if the migration progress delta for the source secondary volume
is YES, copy data from the source secondary volume to the target
secondary volume and change the migration progress delta of the address
of the target secondary volume to NO.

15. The first storage system according to claim 11, wherein each storage
system includes a pool for storing the difference data for the volumes in
said each storage system; wherein the location information for each
difference data identifies the location of said each difference data in
the pool; wherein the location information for each difference data is
associated with a secondary volume which has said each difference data
with respect to a corresponding primary volume; and wherein, for
migration from a source primary volume and a corresponding source
secondary volume which establish a pair of source volumes in the first
storage system to a target primary volume and a corresponding target
secondary volume which establish a pair of target volumes in a target
storage system, the first storage system further comprises a local copy
control module configured to manage local copy difference information
between each source primary volume and each corresponding source
secondary volume which establish a pair; and wherein the migration
control module is configured, if the local copy difference information
indicates there is difference data between a pair of source volumes, copy
the difference data for the pair of source volumes from a pool in the
first storage system to a pool in a target storage system using the
location information associated with the source secondary volume of the
pair of source volumes.

16. A second storage system in a system of a plurality of storage
systems, the second storage system comprising a processor; a memory; and
a migration control module, the migration control module being configured
to: migrate a set of source primary and secondary volumes from one or
more source storage systems to the second storage system by managing and
copying, between the one or more source storage systems to the second
storage system, a plurality of same data and a plurality of difference
data between the source primary and secondary volumes and location
information of each of the plurality of difference data, the location
information identifying a location of the difference data in the source
primary or secondary volume associated with the difference data; wherein
each source secondary volume which corresponds to a source primary
volume, if said each source secondary volume contains data, has a same
data as the source primary volume and, if said each source secondary
volume is not synchronized with the source primary volume, further has a
difference data with respect to the source primary volume.

17. The second storage system according to claim 16, wherein the
migration control module is configured to copy each same data of the
plurality of same data from a source primary volume for said each same
data to a corresponding target primary volume and a corresponding target
secondary volume in the second storage system; and wherein the migration
control module is configured to copy each difference data of the
plurality of difference data from a source secondary volume for said
difference data to a corresponding target secondary volume in the second
storage system.

18. The second storage system according to claim 16, wherein the location
information of each difference data of the plurality of difference data
comprises a delta bitmap identifying the location of said each difference
data in the source primary or secondary volume associated with the
difference data; wherein one source primary volume has a plurality of
corresponding source secondary volumes to establish multiple pairs for
the same source primary volume, each pair of the multiple pairs having a
delta bitmap identifying the location of any difference data for said
each pair; and wherein migrating the source primary volume and the
plurality of corresponding source secondary volumes comprises copying
same data and difference data, for the source primary volume and the
plurality of corresponding source secondary volumes, to a target primary
volume and a plurality of corresponding target secondary volumes in the
second storage subsystem, based on the delta bitmap of each pair of the
multiple pairs.

19. The second storage system according to claim 16, wherein for
migration from a source primary volume and a corresponding source
secondary volume which establish a pair of source volumes in a source
storage system to a target primary volume and a corresponding target
secondary volume which establish a pair of target volumes in the second
storage system, the second storage system further comprises a local copy
control module configured to manage local copy difference information
between each target primary volume and each corresponding target
secondary volume which establish a pair; and wherein the migration
control module is configured to: manage migration progress between each
source volume and each corresponding target volume using a migration
progress management table which shows, for an address of one or both of
the source volumes of each pair, a migration progress delta which is
initially set to YES and is changed to NO when a copy for migration from
source to target is finished on the address; if the migration progress
delta for the source primary volume is YES, copy data from the source
primary volume to the target primary volume and change the migration
progress delta of the address of the target primary volume to NO,
wherein, if the local copy difference information indicates there is no
difference data between the target primary volume and the target
secondary volume, the local copy control module is configured to copy the
data from the target primary volume to the target secondary volume and
change the migration progress delta of the address of the target
secondary volume to NO; and if the migration progress delta for the
source secondary volume is YES, copy data from the source secondary
volume to the target secondary volume and change the migration progress
delta of the address of the target secondary volume to NO.

20. The second storage system according to claim 16, wherein each storage
system includes a pool for storing the difference data for the volumes in
said each storage system; wherein the location information for each
difference data identifies the location of said each difference data in
the pool; wherein the location information for each difference data is
associated with a secondary volume which has said each difference data
with respect to a corresponding primary volume; and wherein, for
migration from a source primary volume and a corresponding source
secondary volume which establish a pair of source volumes in a source
storage system to a target primary volume and a corresponding target
secondary volume which establish a pair of target volumes in the second
storage system, the second storage system further comprises a local copy
control module configured to manage local copy difference information
between each target primary volume and each corresponding target
secondary volume which establish a pair; and wherein the migration
control module is configured to obtain from the source storage system
local copy difference information between the source primary volume and
the source secondary volume which establish the pair of source volumes,
and, if the obtained local copy difference information indicates there is
difference data between the pair of source volumes, copy the difference
data for the pair of source volumes from a pool in the first storage
system to a pool in a target storage system using the location
information associated with the source secondary volume of the pair of
source volumes.

Description:

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to storage systems and,
more particularly, to methods and apparatus for reducing traffic on data
migration.

[0002] Non-disruptive volume and path migration technology is known. See,
e.g., U.S. Pat. No. 7,991,860. The technology is for a simplex
(non-function-applied) volume, but it can be easily extended to function
applied volume such as, for instance, local copy applied volume. The
method involves migrating all volumes which establish a pair or
consistency group simultaneously, establishing a pair or a group using
migration target volumes with the same configuration of migration source
volumes, and succeeds the status and other information relating to the
pair and group to the migration target.

[0003] Generally, a narrow connection between the migration source and the
target storage devices makes the migration slow. It is difficult to
install new switch devices to increase traffic performance because it
increases cost.

BRIEF SUMMARY OF THE INVENTION

[0004] Exemplary embodiments of the invention provide a technique to
reduce the traffic between the storage devices during data migration.
Generally the connection between storage devices is tighter/narrower than
that the internal connection of a storage device. The narrower connection
renders data migration slower. Embodiments of this invention make it
possible to offload traffic load between storage devices to the internal
connection of a storage device. According to one embodiment, a data
migration method migrates all volumes which establish a pair or a
consistency group simultaneously. It establishes a pair or a group using
migration target volumes with the same configuration as migration source
volumes. The storage device finds or makes deduplicated data before
migration. The storage device transfers only the deduplicated data and
difference data just once. After migration target storage device copies
the data, it expands the deduplication if necessary (i.e., restores the
original configuration and data storing status). The technique can reduce
migration transfer load on local copy/snapshot used environment.

[0005] In accordance with an aspect of the present invention, a system
comprises a plurality of storage systems which are operable to migrate a
set of primary and secondary volumes between the plurality of storage
systems by managing and copying, between the plurality of storage
systems, a plurality of same data and a plurality of difference data
between the primary and secondary volumes and location information of
each of the plurality of difference data, the location information
identifying a location of the difference data in the primary or secondary
volume associated with the difference data. Each secondary volume which
corresponds to a primary volume, if said each source secondary volume
contains data, has a same data as the primary volume and, if said each
secondary volume is not synchronized with the primary volume, further has
a difference data with respect to the primary volume.

[0006] In some embodiments, the plurality of storage systems are operable
to copy each same data of the plurality of same data from a source
primary volume for said each same data to a corresponding target primary
volume and a corresponding target secondary volume. The corresponding
target primary volume and the corresponding target secondary volume are
disposed in a target storage system. The plurality of storage systems are
operable to copy each difference data of the plurality of difference data
from a source secondary volume for said each difference data to a
corresponding target secondary volume, if data in the corresponding
target secondary volume has not been updated in the target storage system
since the difference data is stored in the source secondary volume.

[0007] In specific embodiments, the plurality of storage systems are
operable to copy each difference data of the plurality of difference data
from a source secondary volume for said each difference data to a
corresponding target secondary volume. The location information of each
difference data of the plurality of difference data comprises a delta
bitmap identifying the location of said each difference data in the
primary or secondary volume associated with the difference data. A source
primary volume has a plurality of corresponding source secondary volumes
to establish multiple pairs for the same source primary volume, each pair
of the multiple pairs having a delta bitmap identifying the location of
any difference data for said each pair. Migrating the source primary
volume and the plurality of corresponding source secondary volumes
comprises copying same data and difference data for the source primary
volume and the plurality of corresponding source secondary volumes, to a
target primary volume and a plurality of corresponding target secondary
volumes, based on the delta bitmap of each pair of the multiple pairs.

[0008] In some embodiments, for migration from a source primary volume and
a corresponding source secondary volume which establish a pair of source
volumes in a source storage system to a target primary volume and a
corresponding target secondary volume which establish a pair of target
volumes in a target storage system, the plurality of storage systems are
operable to: manage local copy difference information between each
primary volume and each corresponding secondary volume which establish a
pair; manage migration progress between each source volume and each
corresponding target volume using a migration progress management table
which shows, for an address of one or both of the volumes of each pair, a
migration progress delta which is initially set to YES and is changed to
NO when a copy for migration from source to target is finished on the
address; if the migration progress delta for the source primary volume is
YES, copy data from the source primary volume to the target primary
volume and change the migration progress delta of the address of the
target primary volume to NO, and, if the local copy difference
information indicates there is no difference data between the target
primary volume and the target secondary volume, copy the data from the
source primary volume to the target secondary volume and change the
migration progress delta of the address of the target secondary volume to
NO; and if the migration progress delta for the source secondary volume
is YES, copy data from the source secondary volume to the target
secondary volume and change the migration progress delta of the address
of the target secondary volume to NO.

[0009] In specific embodiments, each storage system includes a pool for
storing the difference data for the volumes in said each storage system,
and the location information for each difference data identifies the
location of said each difference data in the pool. The location
information for each difference data is associated with a secondary
volume which has said each difference data with respect to a
corresponding primary volume. The plurality of storage systems are
configured, for migration from a source primary volume and a
corresponding source secondary volume which establish a pair of source
volumes in a source storage system to a target primary volume and a
corresponding target secondary volume which establish a pair of target
volumes in a target storage system, to: manage local copy difference
information between each primary volume and each corresponding secondary
volume which establish a pair; and if the local copy difference
information indicates there is difference data between the pair of source
volumes, copy the difference data for the pair of source volumes from a
pool in the source storage system to a pool in the target storage system
using the location information associated with the source secondary
volume of the pair of source volumes. A source primary volume has a
plurality of corresponding source secondary volumes to establish multiple
pairs for the same source primary volume, each corresponding source
secondary volume being associated with the location information for any
difference data with respect to the source primary volume. The plurality
of storage systems are configured, after the difference data is copied
from the pool in the source storage system to the pool in the target
storage system, to associate the location information for the difference
data in the pool in the target storage system with each corresponding
target secondary volume in the target storage system.

[0010] Another aspect of the invention is directed to a first storage
system in a system of a plurality of storage systems. The first storage
system comprises a processor; a memory; and a migration control module.
The migration control module is configured to migrate a set of source
primary and secondary volumes from the first storage system to one or
more target storage systems by managing and copying, between the first
storage system and the one or more target storage systems, a plurality of
same data and a plurality of difference data between the source primary
and secondary volumes and location information of each of the plurality
of difference data, the location information identifying a location of
the difference data in the source primary or secondary volume associated
with the difference data. Each source secondary volume which corresponds
to a source primary volume, if said each source secondary volume contains
data, has a same data as the source primary volume and, if said each
source secondary volume is not synchronized with the source primary
volume, further has a difference data with respect to the source primary
volume.

[0011] In some embodiments, the migration control module is configured to
copy each same data of the plurality of same data from a source primary
volume for said each same data to a corresponding target primary volume
and a corresponding target secondary volume in a target storage system.
The migration control module is configured to copy each difference data
of the plurality of difference data from a source secondary volume for
said difference data to a corresponding target secondary volume in a
target storage system.

[0012] In specific embodiments, the location information of each
difference data of the plurality of difference data comprises a delta
bitmap identifying the location of said each difference data in the
source primary or secondary volume associated with the difference data.
One source primary volume has a plurality of corresponding source
secondary volumes to establish multiple pairs for the same source primary
volume, each pair of the multiple pairs having a delta bitmap identifying
the location of any difference data for said each pair. Migrating the
source primary volume and the plurality of corresponding source secondary
volumes comprises copying same data and difference data, for the source
primary volume and the plurality of corresponding source secondary
volumes, to a target primary volume and a plurality of corresponding
target secondary volumes in a target storage subsystem, based on the
delta bitmap of each pair of the multiple pairs.

[0013] In some embodiments, for migration from a source primary volume and
a corresponding source secondary volume which establish a pair of source
volumes in the first storage system to a target primary volume and a
corresponding target secondary volume which establish a pair of target
volumes in a target storage system, the first storage system further
comprises a local copy control module configured to manage local copy
difference information between each source primary volume and each
corresponding source secondary volume which establish a pair. The
migration control module is configured to: manage migration progress
between each source volume and each corresponding target volume using a
migration progress management table which shows, for an address of one or
both of the source volumes of each pair, a migration progress delta which
is initially set to YES and is changed to NO when a copy for migration
from source to target is finished on the address; if the migration
progress delta for the source primary volume is YES, copy data from the
source primary volume to the target primary volume and change the
migration progress delta of the address of the target primary volume to
NO, and obtain from the target storage system local copy difference
information between the target primary volume and the target secondary
volume, and, if the obtained local copy difference information indicates
there is no difference data between the target primary volume and the
target secondary volume, copy the data from the source primary volume to
the target secondary volume and change the migration progress delta of
the address of the target secondary volume to NO; and if the migration
progress delta for the source secondary volume is YES, copy data from the
source secondary volume to the target secondary volume and change the
migration progress delta of the address of the target secondary volume to
NO.

[0014] In specific embodiments, each storage system includes a pool for
storing the difference data for the volumes in said each storage system.
The location information for each difference data identifies the location
of said each difference data in the pool. The location information for
each difference data is associated with a secondary volume which has said
each difference data with respect to a corresponding primary volume. For
migration from a source primary volume and a corresponding source
secondary volume which establish a pair of source volumes in the first
storage system to a target primary volume and a corresponding target
secondary volume which establish a pair of target volumes in a target
storage system, the first storage system further comprises a local copy
control module configured to manage local copy difference information
between each source primary volume and each corresponding source
secondary volume which establish a pair. The migration control module is
configured, if the local copy difference information indicates there is
difference data between a pair of source volumes, copy the difference
data for the pair of source volumes from a pool in the first storage
system to a pool in a target storage system using the location
information associated with the source secondary volume of the pair of
source volumes.

[0015] Another aspect of this invention is directed to a second storage
system in a system of a plurality of storage systems. The second storage
system comprises a processor; a memory; and a migration control module.
The migration control module is configured to migrate a set of source
primary and secondary volumes from one or more source storage systems to
the second storage system by managing and copying, between the one or
more source storage systems to the second storage system, a plurality of
same data and a plurality of difference data between the source primary
and secondary volumes and location information of each of the plurality
of difference data, the location information identifying a location of
the difference data in the source primary or secondary volume associated
with the difference data. Each source secondary volume which corresponds
to a source primary volume, if said each source secondary volume contains
data, has a same data as the source primary volume and, if said each
source secondary volume is not synchronized with the source primary
volume, further has a difference data with respect to the source primary
volume.

[0016] In some embodiments, the migration control module is configured to
copy each same data of the plurality of same data from a source primary
volume for said each same data to a corresponding target primary volume
and a corresponding target secondary volume in the second storage system.
The migration control module is configured to copy each difference data
of the plurality of difference data from a source secondary volume for
said difference data to a corresponding target secondary volume in the
second storage system.

[0017] In specific embodiments, the location information of each
difference data of the plurality of difference data comprises a delta
bitmap identifying the location of said each difference data in the
source primary or secondary volume associated with the difference data.
One source primary volume has a plurality of corresponding source
secondary volumes to establish multiple pairs for the same source primary
volume, each pair of the multiple pairs having a delta bitmap identifying
the location of any difference data for said each pair. Migrating the
source primary volume and the plurality of corresponding source secondary
volumes comprises copying same data and difference data, for the source
primary volume and the plurality of corresponding source secondary
volumes, to a target primary volume and a plurality of corresponding
target secondary volumes in the second storage subsystem, based on the
delta bitmap of each pair of the multiple pairs.

[0018] In some embodiments, for migration from a source primary volume and
a corresponding source secondary volume which establish a pair of source
volumes in a source storage system to a target primary volume and a
corresponding target secondary volume which establish a pair of target
volumes in the second storage system, the second storage system further
comprises a local copy control module configured to manage local copy
difference information between each target primary volume and each
corresponding target secondary volume which establish a pair. The
migration control module is configured to: manage migration progress
between each source volume and each corresponding target volume using a
migration progress management table which shows, for an address of one or
both of the source volumes of each pair, a migration progress delta which
is initially set to YES and is changed to NO when a copy for migration
from source to target is finished on the address; if the migration
progress delta for the source primary volume is YES, copy data from the
source primary volume to the target primary volume and change the
migration progress delta of the address of the target primary volume to
NO, wherein, if the local copy difference information indicates there is
no difference data between the target primary volume and the target
secondary volume, the local copy control module is configured to copy the
data from the target primary volume to the target secondary volume and
change the migration progress delta of the address of the target
secondary volume to NO; and if the migration progress delta for the
source secondary volume is YES, copy data from the source secondary
volume to the target secondary volume and change the migration progress
delta of the address of the target secondary volume to NO.

[0019] In specific embodiments, each storage system includes a pool for
storing the difference data for the volumes in said each storage system.
The location information for each difference data identifies the location
of said each difference data in the pool. The location information for
each difference data is associated with a secondary volume which has said
each difference data with respect to a corresponding primary volume. For
migration from a source primary volume and a corresponding source
secondary volume which establish a pair of source volumes in a source
storage system to a target primary volume and a corresponding target
secondary volume which establish a pair of target volumes in the second
storage system, the second storage system further comprises a local copy
control module configured to manage local copy difference information
between each target primary volume and each corresponding target
secondary volume which establish a pair. The migration control module is
configured to obtain from the source storage system local copy difference
information between the source primary volume and the source secondary
volume which establish the pair of source volumes, and, if the obtained
local copy difference information indicates there is difference data
between the pair of source volumes, copy the difference data for the pair
of source volumes from a pool in the first storage system to a pool in a
target storage system using the location information associated with the
source secondary volume of the pair of source volumes.

[0020] These and other features and advantages of the present invention
will become apparent to those of ordinary skill in the art in view of the
following detailed description of the specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 illustrates an example of a physical and logical hardware
configuration of a system in which the method and apparatus of the
invention may be applied according to a first embodiment of the
invention.

[0022]FIG. 2 illustrates an example of the logical hardware and local
copy pair configuration of the system of FIG. 1 during migration
according to the first embodiment of the invention.

[0023]FIG. 3 illustrates an example of a Local Copy Pair Management Table
according to the first embodiment of the invention.

[0024]FIG. 4 illustrates an example of a Local Copy Delta Management
Table according to the first embodiment of the invention.

[0025]FIG. 5 illustrates an example of a Migration Progress Management
Table according to the first embodiment of the invention.

[0026]FIG. 6 is an example of a flow diagram illustrating the process of
a Migration Progress Program according to the first embodiment of the
invention.

[0027] FIG. 7 shows the source storage subsystem and the target storage
subsystem to illustrate an example of the migration process based on the
Migration Progress Program as described above in connection with FIG. 6.

[0028] FIG. 8 illustrates an example of the physical and logical hardware
configuration of a system in which the method and apparatus of the
invention may be applied according to a second embodiment of the
invention.

[0029]FIG. 9 illustrates an example of the logical hardware and local
copy pair configuration of the system of FIG. 8 during migration
according to the second embodiment of the invention.

[0030]FIG. 10 is an example of a flow diagram illustrating the process of
a Migration Progress Program according to the second embodiment of the
invention.

[0031]FIG. 11 illustrates an example of the physical and logical hardware
configuration of a system in which the method and apparatus of the
invention may be applied according to a third embodiment of the
invention.

[0032]FIG. 12 illustrates an example of the primary volume, secondary
volumes, and pool configuration of the system according to the third
embodiment of the invention.

[0033]FIG. 13 illustrates an example of a Snapshot Pair Management Table
according to the third embodiment of the invention.

[0034]FIG. 14 illustrates an example of a Snapshot Primary Volume Delta
Management Table according to the third embodiment of the invention.

[0035]FIG. 15 illustrates an example of a Snapshot Secondary Volume Delta
Management Table according to the third embodiment of the invention.

[0036]FIG. 16 illustrates an example of a Snapshot Pool Management Table
144 according to the third embodiment of the invention.

[0037]FIG. 17 is an example of a flow diagram illustrating the process of
a Migration Progress Program according to the third embodiment of the
invention.

DETAILED DESCRIPTION OF THE INVENTION

[0038] In the following detailed description of the invention, reference
is made to the accompanying drawings which form a part of the disclosure,
and in which are shown by way of illustration, and not of limitation,
exemplary embodiments by which the invention may be practiced. In the
drawings, like numerals describe substantially similar components
throughout the several views. Further, it should be noted that while the
detailed description provides various exemplary embodiments, as described
below and as illustrated in the drawings, the present invention is not
limited to the embodiments described and illustrated herein, but can
extend to other embodiments, as would be known or as would become known
to those skilled in the art. Reference in the specification to "one
embodiment," "this embodiment," or "these embodiments" means that a
particular feature, structure, or characteristic described in connection
with the embodiment is included in at least one embodiment of the
invention, and the appearances of these phrases in various places in the
specification are not necessarily all referring to the same embodiment.
Additionally, in the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding of the
present invention. However, it will be apparent to one of ordinary skill
in the art that these specific details may not all be needed to practice
the present invention. In other circumstances, well-known structures,
materials, circuits, processes and interfaces have not been described in
detail, and/or may be illustrated in block diagram form, so as to not
unnecessarily obscure the present invention.

[0039] Furthermore, some portions of the detailed description that follow
are presented in terms of algorithms and symbolic representations of
operations within a computer. These algorithmic descriptions and symbolic
representations are the means used by those skilled in the data
processing arts to most effectively convey the essence of their
innovations to others skilled in the art. An algorithm is a series of
defined steps leading to a desired end state or result. In the present
invention, the steps carried out require physical manipulations of
tangible quantities for achieving a tangible result. Usually, though not
necessarily, these quantities take the form of electrical or magnetic
signals or instructions capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at times,
principally for reasons of common usage, to refer to these signals as
bits, values, elements, symbols, characters, terms, numbers,
instructions, or the like. It should be borne in mind, however, that all
of these and similar terms are to be associated with the appropriate
physical quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise, as apparent from the
following discussion, it is appreciated that throughout the description,
discussions utilizing terms such as "processing," "computing,"
"calculating," "determining," "displaying," or the like, can include the
actions and processes of a computer system or other information
processing device that manipulates and transforms data represented as
physical (electronic) quantities within the computer system's registers
and memories into other data similarly represented as physical quantities
within the computer system's memories or registers or other information
storage, transmission or display devices.

[0040] The present invention also relates to an apparatus for performing
the operations herein. This apparatus may be specially constructed for
the required purposes, or it may include one or more general-purpose
computers selectively activated or reconfigured by one or more computer
programs. Such computer programs may be stored in a computer-readable
storage medium, such as, but not limited to optical disks, magnetic
disks, read-only memories, random access memories, solid state devices
and drives, or any other types of media suitable for storing electronic
information. The algorithms and displays presented herein are not
inherently related to any particular computer or other apparatus. Various
general-purpose systems may be used with programs and modules in
accordance with the teachings herein, or it may prove convenient to
construct a more specialized apparatus to perform desired method steps.
In addition, the present invention is not described with reference to any
particular programming language. It will be appreciated that a variety of
programming languages may be used to implement the teachings of the
invention as described herein. The instructions of the programming
language(s) may be executed by one or more processing devices, e.g.,
central processing units (CPUs), processors, or controllers.

[0041] Exemplary embodiments of the invention, as will be described in
greater detail below, provide apparatuses, methods and computer programs
for reducing traffic on data migration.

First Embodiment

[0042]FIG. 1 illustrates an example of a physical and logical hardware
configuration of a system in which the method and apparatus of the
invention may be applied according to a first embodiment of the
invention. The system includes a host computer 300 coupled via switch
200a to storage subsystems 100a, 100b, which are connected via switch
200b. Each storage subsystem 100a, 100b is a type of computer system
having processor(s), memory, ports, and disks. It receives an I/O from a
host computer and another storage subsystem via port 101. It sends an I/O
to another storage subsystem via port 102. Programs and tables to control
the storage subsystem are stored in the memory and executed by the
processor(s). Volumes 110a and 110b are controlled by the storage
subsystem and the data is stored into the disks. The volumes 110a, 110b
establish a local copy pair as a primary volume 110a and a secondary
volume 110b. If a storage user orders to resynchronize the pair, the data
of the primary volume 110a is copied to the secondary volume 110b. The
management and control of the local copy pair is operated by a Local Copy
Control 120 which is stored in the memory. The volumes 110a, 110b are
migration source volumes to be migrated to volumes 111a and 111b as
discussed further below. The volume 111a and 111b are migration target
volumes to be migrated from the migration source volumes 110a and 110b.
More specifically, the data of the source primary volume 110a is migrated
to the target primary volume 111a, and the data of the source secondary
volume 110b is migrated to the target secondary volume 111b. The
management and control of the migration is operated by a Migration
Control 130 which is stored in the memory. During the migration, if a
migration target volume receives an I/O request, it transfers the I/O
request to its migration source volume. After the migration, both data
and I/O operation are migrated to the migration target volume.

[0043] The Local Copy Control 120 manages and controls local copy. It
needs a pair established by two volumes in a storage subsystem. One
volume is a primary volume the other volume is a secondary volume.
Generally it copies data from the primary volume to the secondary volume.
The start of the copy is ordered by a storage user.

[0044] The Migration Control 130 manages and controls volume migration. It
needs a pair established by two volumes on different storage subsystems.
One volume is a source volume the other volume is a target volume. It
copies data and changes a path from the source volume to the target
volume. The start of the migration is ordered by a storage user.

[0045] The host computer 300 is a type of computer system having
processor(s), memory, and ports. It sends an I/O to the storage subsystem
via port 301. The switches 200a and 200b have ports 201 which transfer
I/O among the host port 301 and the storage subsystem ports 101, 102. In
this embodiment, the switch 200a and 200b are independent devices, but
they can be consolidated into a single device.

[0046]FIG. 2 illustrates an example of the logical hardware and local
copy pair configuration of the system of FIG. 1 during migration
according to the first embodiment of the invention. The source volumes
110a and 110b establishes a local copy pair in the source storage
subsystem 100a. Before the start of the migration, the source volume 110a
and 110b establish a local copy pair. After the migration, it is expected
that the pair configuration also is migrated to the target volumes. As
such, the target storage subsystem 100b creates the target volumes 111a
and 111b. The target storage subsystem 100b starts the migration, and
changes the path between the host computer 300 and the source storage
subsystem 100a to a path between the host computer 300 and the target
storage subsystem 100b. The target storage subsystem 100b copies the pair
status between the source volumes 110a and 110b and applies the pair
status to the target volumes 111a and 111b.

[0047]FIG. 3 illustrates an example of a Local Copy Pair Management Table
121 according to the first embodiment of the invention. This table is
used by and may be included in the Local Copy Control 120 to manage the
pair configuration and status between volumes. The table is stored in the
source storage subsystem 100a to be used for managing the pair of source
volumes 110a and 110b. The table is stored in the target storage
subsystem 100b to be used for managing the pair of target volume 111a and
111b. The table includes columns of Pair Number 121-1 containing an ID of
a pair, Status 121-2 indicating the status of the pair, Primary Volume
(PVOL) Number 121-3 containing an ID of the primary volume of the pair,
and Secondary Volume (SVOL) Number 121-4 containing an ID of the
secondary volume of the pair. For the Status column, the "PSUS" status
means the primary and the secondary volumes are independent. During this
status, the Local Copy Control 120 records a write accessed area of the
primary volume and the secondary volume. The "COPY" and "PAIR" status
each mean that the primary and the secondary volumes are synchronized.
During this status, the Local Copy Control 120 copies data from the
primary volume to the secondary volume which is located in the write
accessed area and forbids access to the secondary volume. The "SMPL"
status means the pair is not established yet.

[0048]FIG. 4 illustrates an example of a Local Copy Delta Management
Table 122 according to the first embodiment of the invention. This table
is used by and may be included in the Local Copy Control 120. Each pair
listed in the Copy Pair Management Table 121 has this Local Copy Delta
Management Table 122. It manages the difference between the primary
volume and secondary volume which establish a pair. The table has columns
of Address 122-1 and Delta Information 122-2. The Address 122-1 is the
address of a primary volume or a secondary volume of the pair. For the
Delta Information 122-2, the initial record (when the pair status changes
to "PSUS" from other pair status) is "No" on all addresses. When a
primary volume and/or a secondary volume receives a write I/O, the status
changes to "Yes." When a copy from a primary volume to a secondary volume
has been finished on the address on "COPY" or "PAIR" status, the record
changes to "No."

[0049] One aspect of the invention is to manage the migration of each pair
of primary volume and secondary volume which have same data and
difference data in general (there will be no difference data if they are
synchronized). Ideally, it is preferably, during migration of each pair
of primary volume and secondary volume, to copy the same data to the
target only once and, if there is any difference data, to copy the
difference data to the target only once, thereby reducing migration
transfer load. Embodiments of this invention enable the system to do so.

[0050]FIG. 5 illustrates an example of a Migration Progress Management
Table 131 according to the first embodiment of the invention. This table
is used by and may be included in the Migration Control 130. Each
migration target volume has this table. The table has columns of Address
131-1 and Delta Information 131-2. The Address 131-1 is the address of a
primary volume or a secondary volume of the pair. For the Delta
Information 131-2, the initial record (when the migration starts) is
"Yes" on all addresses. When a copy for migration has been finished on
the address, the record changes to "No."

[0051]FIG. 6 is an example of a flow diagram illustrating the process of
a Migration Progress Program 132 according to the first embodiment of the
invention. This program is included in the Migration Control 130. It
copies data from a source volume to a target volume which establish a
local copy pair. The program starts at step 132-1. It creates migration
target volumes 111a and 111b with local copy pair establishment and sets
the pair status to "PSUS" (132-2). In step 132-3, it changes the paths
between the host computer 300 and the source volumes 110a and 110b to
paths between the host computer 300 and the target volumes 111a and 111b.
In step 132-4, it gets the local copy pair status in the Local Copy Pair
Management Table 121 of the source storage subsystem 100a. In step 132-5,
it changes the pair status of the target volume 111a and 111b pair to the
same as the source volume 110a and 110b pair. In step 132-6, the program
gets the local copy difference information (delta bitmap) in the Local
Copy Delta Management Table 122 of the source storage subsystem 100a. In
step 132-7, it combines the local copy difference information from the
Local Copy Delta Management Tables 122 of the source storage subsystem
100a into that of the target storage subsystem100b. If both records are
"Yes," the program stores "Yes." If both records are "No," the program
stores "No." If one is "Yes" and the other is "No," the program stores
"Yes." In step 132-8, if the delta information 131-2 of an address of a
migration source primary volume 110a is "Yes," the program reads the data
of the address from a migration source primary volume 110a, and copies
the data to a migration target primary volume 111a and changes the delta
information 131-2 of the address of the target primary volume 111a to
"No." If the delta information 122-2 of an address of a pair stored in
the target storage subsystem 100b is "No" or if the pair status is "PAIR"
or "COPY", the program copies the data to a migration target secondary
volume 111b and changes the delta information 131-2 of the address of the
target secondary volume 111b to "No" also. In step 132-9, if the delta
information 131-2 of an address of a migration source secondary volume
110b is "Yes," the program reads data of the address from a migration
source secondary volume 110b, and copies the data to a migration target
secondary volume 111b and changes the delta information 131-2 of the
address of the target secondary volume 111b to "No." In step 132-10, the
program releases the pair of migration source volumes 110a and 110b and
deletes the migration source volumes 110a and 110b. In step 132-11, the
program ends.

[0052] During step 132-5 and step 132-7, write I/O may occur onto the
migration target volumes. However it can keep a record of the write I/O
area on the Local Copy Delta Management Table 122 stored in a storage
subsystem 100b by the method described in step 132-7.

[0053] To protect from data lost by some failure on migration process, the
Migration Program 132 can replicate write I/O which a migration source
volume receives to a migration target volume.

[0054] If a pair status is changed during migration, it stops the
migration, resets the migration configuration, and restarts the
migration.

[0055] FIG. 7 shows the source storage subsystem 100a and the target
storage subsystem 100b to illustrate an example of the migration process
based on the Migration Progress Program 132 as described above in
connection with FIG. 6.

Second Embodiment

[0056] FIG. 8 illustrates an example of the physical and logical hardware
configuration of a system in which the method and apparatus of the
invention may be applied according to a second embodiment of the
invention. Only differences from the first embodiment of FIG. 1 are
described. The source storage subsystem 100a has a migration source
volume 110c, and the target storage subsystem 100b has a migration target
volume 111c for the migration source volume 110c.

[0057]FIG. 9 illustrates an example of the logical hardware and local
copy pair configuration of the system of FIG. 8 during migration
according to the second embodiment of the invention. The secondary
volumes 110b and 110c share the same primary volume 110a in the source
storage subsystem 100a. The primary volume 110a and secondary volume 110b
establish a local copy pair, and the primary volume 110a and secondary
volume 110c also establish a local copy pair.

[0058]FIG. 10 is an example of a flow diagram illustrating the process of
a Migration Progress Program 132' according to the second embodiment of
the invention. This Migration Progress Program 132' is included in the
Migration Control 130 instead of Migration Progress Program 132 of first
embodiment. It copies data from a source volume to a target volume which
establish a local copy pair. The program starts at step 132'-1. In step
132'-2, it creates migration target volumes 111a, 111b, 111c with local
copy pair establishments, and sets each pair status to "PSUS." In step
132'-3, it changes the path between the host computer 300 and the source
volumes 110a,110b, 110c to the path between the host computer 300 and the
target volumes 111a, 111b, 111c. In step 132'-4, it gets each local copy
pair status in the Local Copy Pair Management Table 121 of the source
storage subsystem 100a. In step 132'-5, it change each pair status of the
target volumes 111a and 111b and the target volumes 111a and 111c pair to
the same as that of the source volumes 110a and 110b pair and the source
volumes 110a and 110c pair.

[0059] In step 132'-6, the program gets each piece of the local copy
difference information in the Local Copy Delta Management Table 122 of
the source storage subsystem 100a. In step 132'-7, it combines the local
copy difference information from the Local Copy Delta Management Tables
122 of the source storage subsystem 100a into that of the target storage
subsystem 100b. If both records are "Yes," the program stores "Yes." If
both records are "No," the program stores "No." If one is "Yes" and the
other is "No," the program stores "Yes." In step 132'-8, if the delta
information 131-2 of an address of a migration source primary volume 110a
is "Yes," the program reads data of the address from a migration source
primary volume 110a, and copies the data to a migration target primary
volume 111a and changes the delta information 131-2 of the address of the
target primary volume 111a to "No." If the delta information 122-2 of an
address of a pair stored in the target storage subsystem 100b is "No" or
the pair status is "PAIR" or "COPY," the program copies the data to a
migration target secondary volume 111b or 111c and changes the delta
information 131-2 of the address of the copied target secondary volume to
"No" also. In step 132'-9, if the delta information 131-2 of an address
of a migration source secondary volume 110b is "Yes," the program reads
data of the address from a migration source secondary volume 110b, and
copies the data to a migration target secondary volume 111b and changes
the delta information 131-2 of the address of the target secondary volume
111b to "No." This operation applies to the other source secondary volume
110c also. In step 132'-10, the program releases the pairs of volumes
110a and 110b, and 110a and 110c, and deletes the migration source
volumes 110a, 110b and 110c. In step 132'-11, the program ends.

Third Embodiment

[0060]FIG. 11 illustrates an example of the physical and logical hardware
configuration of a system in which the method and apparatus of the
invention may be applied according to a third embodiment of the
invention. Only differences from the second embodiment of FIG. 8 are
described. Each storage subsystem 100a, 100b has a pool 150 to store the
difference data. The difference data is the result of a previous data
write I/O that occurs on a primary volume or a secondary volume and the
data has not been synchronized between the primary volume and the
secondary volume. In the second embodiment, a Snapshot Control 140 is
stored in the memory of each storage subsystem instead of the Local Copy
Control 120. The Snapshot Control 140 manages and controls logical
snapshot. It needs a pair established by two volumes in a storage
subsystem. One volume is a primary volume the other volume is a secondary
volume. Generally it evacuates old data from the primary volume to the
secondary volume when write I/O occurs on the primary volume and/or
secondary volume. The start of the Snapshot Control process is ordered by
a storage user. Two or more secondary volumes can share a same primary
volume.

[0061]FIG. 12 illustrates an example of the primary volume, secondary
volumes, and pool configuration of the system according to the third
embodiment of the invention. The primary volume 110a is separated into a
plurality of chunks 110a-1. The secondary volume 110b is separated into a
plurality of chunks 110b-1. The secondary volume 110c is separated into a
plurality of chunks 110c-1. The pool 150 is separated into a plurality of
chunks 150-1. A secondary volume chunk 110b-1 or 110c-1 refers to a
primary volume chunk 110a-1 or a pool chunk 150-1. Two or more secondary
volume chunks can refer to the same pool chunk 150-1. When a read I/O
occurs on a secondary volume, the system reads data of a primary volume
chunk 110a-1 or a pool chunk 150-1 to which the secondary volume chunk
110b on the accessed area refers. When a write I/O occurs on a primary
volume, it copies current data of the primary volume chunk 110a-1 onto a
pool chunk 150-1 if one or more secondary volume chunks 110b-1 or 110c-1
refer to the primary volume chunk 110a-1, and changes the reference to
the pool chunk 150-1. When a write I/O occurs on a secondary volume, it
copies data of a pool chunk 150-1 onto another chunk 150-1 if one or more
secondary volume chunks 110b-1 and 110c-1 refer the chunk 150-1, and
change the reference to the other chunk 150-1.

[0062]FIG. 13 illustrates an example of a Snapshot Pair Management Table
141 according to the third embodiment of the invention. This table is
used by and may be included in the Snapshot Control 140. It manages the
pair configuration and status between volumes. The table is stored in a
source storage subsystem 100a and can be used to manage a pair of source
volumes 110a and 110b. The table is stored in a target storage subsystem
100b and can be used to manage a pair of target volumes 111a and 111b.
The table has columns of Pair Number 141-1 as an ID of a pair, Status
141-2 showing the status of the pair, Primary Volume Number 141-3 as an
ID of a primary volume of the pair, and Secondary Volume Number 141-4 as
an ID of a secondary volume of the pair. The "PSUS" status means the
primary and the secondary volumes are independent. During this status,
the Snapshot Control 140 evacuates data of a secondary volume to a pool.
The "COPY" status and "PAIR" status each mean the primary and the
secondary volumes are synchronized. During either status, the Snapshot
Control 140 forbids access to the secondary volume. The "SMPL" status
means the pair is not established yet.

[0063]FIG. 14 illustrates an example of a Snapshot Primary Volume Delta
Management Table 142 according to the third embodiment of the invention.
This table is used by and may be included in the Snapshot Control 140.
Each primary volume in the Snapshot Pair Management Table 141 has this
table. It records the written area. This table has columns of Address
142-1 which is the address of a primary volume, and Delta Information
142-2. The initial record when the pair status changes to "PSUS" from
other pair status is "No" on all addresses. When a primary volume
receives a write I/O and evacuates data to the pool 150, the status
changes to "Yes."

[0064]FIG. 15 illustrates an example of a Snapshot Secondary Volume Delta
Management Table 143 according to the third embodiment of the invention.
This table is used by and may be included in the Snapshot Control 140.
Each secondary volume in the Snapshot Pair Management Table 141 has this
table. It records the written area and address of evacuated data. This
table has columns of Address 143-1 which is the address of a secondary
volume, Delta Information 143-2, and Chunk Pointer or Stored Address
143-3. For the Delta Information 143-2, the initial record when the pair
status changes to "PSUS" from other pair status is "No" on all addresses.
When a primary volume or a secondary volume receives a write I/O and
evacuates data to the pool 150, the status changes to "Yes." The Chunk
pointer 143-3 is the address of the pool 150 which stores evacuated data.

[0065]FIG. 16 illustrates an example of a Snapshot Pool Management Table
144 according to the third embodiment of the invention. This table is
used by and may be included in the Snapshot Control 140. A pool has this
table. It manages free and allocated area in a pool and sharing status of
the area by secondary volumes. This table has columns of Address 144-1
which is the address of a pool, Allocation Information 144-2, and Shared
Information 144-3. For the Allocation Information 144-2, if the area is
allocated to store secondary volume data, the record is "Yes." If the
allocation is released, the record changes to "No." For the Shared
Information 144-3, if two or more chunks of secondary volumes refer the
area, the record is "Yes."

[0066]FIG. 17 is an example of a flow diagram illustrating the process of
a Migration Progress Program 132'' according to the third embodiment of
the invention. The program is included in the Migration Control 130
instead of the Migration Program 132' in the second embodiment. It copies
data from a source volume to a target volume and a source pool to a
target pool. The program starts at step 132''-1. In step 132''-2, the
program creates migration target volumes 111a, 111b and 111c with local
copy pair establishments, and sets each pair status as "PSUS." In step
132''-3, it changes the path between a host computer 300 and source
volumes 110a, 110b, 110c to the path between the host computer 300 and
target volumes 111a, 111b, 111c. In step 132''-4, it gets each local copy
pair status in the Snapshot Pair Management Table 141 of the source
storage subsystem 100a. In step 132''-5, the program changes each pair
status of the target volumes 111a and 111b pair and the target volumes
111a and 111c pair to be the same as the pair status of the target
volumes 110a and 110b pair and the target columes110a and 110c pair. In
step 132''-6, the program gets Delta Information in the Snapshot Primary
Volume Delta Management Table 142 and Snapshot Pool Management Table 144
of the source storage subsystem 100a.

[0067] In step 132''-7, the program combines the Delta Information from
the Snapshot Primary Volume Delta Management Tables 142 of the source
storage subsystem 100a into that of the target storage subsystem 100b. If
both records are "Yes," the program stores "Yes." If both records are
"No," it stores "No." If one is "Yes" and the other is "No," the program
stores "Yes." In step 132''-8, if the delta information 142-2 of an
address of a migration source primary volume 110a is "Yes," the program
reads data of the address from a migration source primary volume 110a,
and copies the data to a migration target primary volume 111a and changes
the delta information 142-2 of the address of the target primary volume
111a to "No." In step 132''-9, if the delta information 143-2 of an
address of a migration source secondary volume 110b is "Yes," the program
reads data of the address from a migration source pool 150, and copies
the data to a pool with allocation and changes the delta information 1312
of the address of the target secondary volume 111b to "No." If the area
of a migration source pool 150 is shared with some other volume, it also
changes the pointer of the Chunk Pointer 143-3 to the allocated area and
changes the Delta Information 143-2 of the address of the target
secondary volume 111b to "No." This operation applies to the other
secondary volume 110c also. In step 132''-10, the program releases the
pairs of source volumes 110a and 110b and source volumes 110a and 110c,
and deletes the migration source volumes 110a, 110b and 110c. In step
132''-11, the program ends.

[0068] In specific embodiments such as the first and third embodiments
described above, each storage subsystem has a local copy control 120 to
manage and control the local copy pair, and a migration control 130 to
control migration. In general, the migration from a source storage
subsystem to a target storage subsystem may be controlled by the
migration control 130 in the source storage subsystem or by the migration
control 130 in the target storage subsystem, or even migration control
130 in both storage subsystems. When migration is controlled by only the
migration control 130 in either the source or target storage subsystem,
that migration control 130 in one storage subsystem may obtain local copy
difference information from the other storage subsystem when it is
needed. In a first example, migration in the first embodiment is
controlled by the migration control 130 in the source storage subsystem
100a. In step 132-8 of FIG. 6, the program copies the migration data to
the migration target secondary volume if the delta information 122-2 of
an address of a pair stored in the target storage subsystem 100b is "No"
or if the pair status is "PAIR" or "COPY." This local copy difference
information of the target storage subsystem will need to be obtained by
the migration control 130 of the source storage subsystem. In a second
example, migration in the third embodiment is controlled by the migration
control 130 in the target storage subsystem 100b. In step 132''-9 of FIG.
17, the program copies data from a migration source pool to a migration
target pool if the delta information 143-2 of an address of a migration
source secondary volume 110b is "Yes." This local copy difference
information of the source storage subsystem will need to be obtained by
the migration control 130 of the target storage subsystem.

[0069] Of course, the system configurations illustrated in FIGS. 1, 8, and
11 are purely exemplary of information systems in which the present
invention may be implemented, and the invention is not limited to a
particular hardware configuration. The computers and storage systems
implementing the invention can also have known I/O devices (e.g., CD and
DVD drives, floppy disk drives, hard drives, etc.) which can store and
read the modules, programs and data structures used to implement the
above-described invention. These modules, programs and data structures
can be encoded on such computer-readable media. For example, the data
structures of the invention can be stored on computer-readable media
independently of one or more computer-readable media on which reside the
programs used in the invention. The components of the system can be
interconnected by any form or medium of digital data communication, e.g.,
a communication network. Examples of communication networks include local
area networks, wide area networks, e.g., the Internet, wireless networks,
storage area networks, and the like.

[0070] In the description, numerous details are set forth for purposes of
explanation in order to provide a thorough understanding of the present
invention. However, it will be apparent to one skilled in the art that
not all of these specific details are required in order to practice the
present invention. It is also noted that the invention may be described
as a process, which is usually depicted as a flowchart, a flow diagram, a
structure diagram, or a block diagram. Although a flowchart may describe
the operations as a sequential process, many of the operations can be
performed in parallel or concurrently. In addition, the order of the
operations may be re-arranged.

[0071] As is known in the art, the operations described above can be
performed by hardware, software, or some combination of software and
hardware. Various aspects of embodiments of the invention may be
implemented using circuits and logic devices (hardware), while other
aspects may be implemented using instructions stored on a
machine-readable medium (software), which if executed by a processor,
would cause the processor to perform a method to carry out embodiments of
the invention. Furthermore, some embodiments of the invention may be
performed solely in hardware, whereas other embodiments may be performed
solely in software. Moreover, the various functions described can be
performed in a single unit, or can be spread across a number of
components in any number of ways. When performed by software, the methods
may be executed by a processor, such as a general purpose computer, based
on instructions stored on a computer-readable medium. If desired, the
instructions can be stored on the medium in a compressed and/or encrypted
format.

[0072] From the foregoing, it will be apparent that the invention provides
methods, apparatuses and programs stored on computer readable media for
reducing traffic on data migration. Additionally, while specific
embodiments have been illustrated and described in this specification,
those of ordinary skill in the art appreciate that any arrangement that
is calculated to achieve the same purpose may be substituted for the
specific embodiments disclosed. This disclosure is intended to cover any
and all adaptations or variations of the present invention, and it is to
be understood that the terms used in the following claims should not be
construed to limit the invention to the specific embodiments disclosed in
the specification. Rather, the scope of the invention is to be determined
entirely by the following claims, which are to be construed in accordance
with the established doctrines of claim interpretation, along with the
full range of equivalents to which such claims are entitled.